Comparison of the piezoelectric response of PVDF composite nanofibers and their films prepared with various additives

In this thesis, PVDF fiber and film materials with piezoelectric properties capable of self-power generation via energy harvesting were produced. The objective is to improve the piezoelectric properties of materials produced with graphene, BN, and SiO2 by obtaining high β phase ratios in the PVDF crystal structure, resulting in increased electricity production, or a higher output voltage. Electrospinning was used to produce fiber materials, and both the operational parameters of the electrospinning process and the parameters influencing the solution properties were evaluated simultaneously. The seven parameters that have a significant effect on the β phase content are: tip-to-collector distance (TCD), solution flow rate, polymer concentration, solvent pair ratio (DMF/acetone), applied voltage value, additive material selection, and additive material weight ratio. The L27 (3^7) orthogonal array is chosen by applying the Taguchi method to seven parameters and three levels, based on the experimental design method. According to this selected orthogonal array design, an optimization study was conducted using analysis of variance (ANOVA) and main effect graphs for signal-to-noise (S/N) ratios. L27 (3^7) orthogonal design applied first, polymer concentration, and additive material selection were found to be the most effective fiber production parameters using the Taguchi method. The second Taguchi L9 (3^2) orthogonal array was chosen as 2 parameters, 3 levels, which were determined to have a significant effect, and the optimal conditions were found as: the tip-to-collector distance 17 cm, the solution flow rate 0.6 ml/h, the polymer concentration 25% by weight, the solvent pair ratio (DMF/acetone) being 1.5, the applied voltage value being 21 kV, and the additive SiO2 and additive material ratio being 0.5 by weight. As a result of the analysis, whose validation experiments were conducted and whose results matched with 98% accuracy, the optimal fiber material with the highest β phase was manufactured. FT-IR, XRD, SEM, EDX, and DSC analyses were performed on fiber mat produced under optimal conditions (OPT-Fiber) and fiber mat produced at the same parameter and level as the reference sample, but without additive material (SAF-Fiber). Output voltage values was measured using an oscilloscope. FT-IR analysis determined that the β phase content of OPT-Fiber mat was 99.9%, while FT-IR analysis determined that the β phase content of neat SAF-Fiber was 86.6%. Using an oscilloscope, the output voltage of OPT-Fiber was measured to be 8.68 V, demonstrating its superior piezoelectric performance in comparison to SAF-Fiber. Due to the low resistance of fiber materials to deformation, it is desired to produce more resilient film materials. Four production parameters, including polymer concentration, additive material selection, weight additive ratio, and press time, were favored during the production of film materials using the solution casting method. In order to provide polarization and direct the dipoles, each material was subjected to a step-wise polarization method of up to 60 MV/m following the completion of film production. Using an experimental design, the parameters that significantly affect the β phase content were identified. Four parameters and three levels of the Taguchi method are used to select the L9 (3^4) orthogonal array. According to this chosen orthogonal array design, an optimization study was conducted using analysis of variance (ANOVA) and the main effect graphs for signal-to-noise ratios (S/N). The optimal conditions were determined to be as: polymer concentration 15% by weight, additive material BN, a ratio of additives by weight of 0.05, and a pressing time 2 hours. As a result of the analysis, for which validation experiments were conducted and the results correlated with 97.5% accuracy, the optimal film material with the highest β phase was manufactured. FT-IR, XRD, and DSC analyses of the film material (OPT-Film) produced under optimal conditions and the film material (SAF-Film) produced at the same parameter and level as the reference sample but without additive material were performed, dielectric constant calculated and the output voltage values was measured using an oscilloscope. FT-IR analysis determined that the β phase content of OPT-Film was 80%, while the β phase content of SAF-Film was 68%. Using an oscilloscope, the output voltage of OPT-Film was measured to be 6.48 V, demonstrating higher performance over SAF-Fiber.